The invention relates to stacker cranes. A conventional stacker crane has a bridge moving along a runway, and a trolley moving along the bridge. A typical trolley runs on top of the bridge, i.e., the entire trolley is located above the top of the bridge. The trolley includes a frame and a turntable rotatable relative to the frame about a vertical axis. The turntable is supported by a rotate bearing on top of the trolley frame. A rotate drive fixed relative to the turntable rotates the turntable relative to the trolley frame.
The conventional stacker crane also includes a mast assembly depending from and fixed to the turntable. The mast assembly includes an upper or rigid mast depending from the turntable, and an intermediate mast moveable vertically along the rigid mast. A carriage is moveable vertically relative to the intermediate mast, and a load engaging mechanism, such as forks or jaws, move with the carriage.
The carriage is raised and lowered by a hoist assembly. The hoist assembly includes a drum which is mounted on the turntable and which moves with the turntable relative to the trolley frame, a drum drive which is mounted on the turntable and which moves with the turntable relative to the trolley frame, a bottom block fixed to the carriage, and a rope or cable wound around the drum and reeved around the bottom block. Rotation of the drum in one direction raises the carriage, and rotation of the drum in the other direction lowers the carriage. When the rotate drive is actuated, the turntable, the mast assembly, the carriage, the load engaging mechanism and the hoist all rotate relative to the trolley frame.